Diversity and distribution of Udotea genus J. V. Lamouroux (Chlorophyta, Udoteaceae) in the Yucatan peninsula littoral, Mexico Author Acosta-Calderón, Julio Adulfo Instituto Politécnico Nacional, Escuela Nacional de Ciencias Biológicas, Departamento de Botánica. Campus Santo Tomas. Carpio y Plan de Ayala, C. P. 11340. Ciudad de México. Author Hernández-Rodríguez, César Instituto Politécnico Nacional, Escuela Nacional de Ciencias Biológicas, Departamento de Microbiología. Campus Santo Tomas. Carpio y Plan de Ayala, C. P. 11340. Ciudad de México Author Mendoza-González, Ángela Catalina Instituto Politécnico Nacional, Escuela Nacional de Ciencias Biológicas, Departamento de Botánica. Campus Santo Tomas. Carpio y Plan de Ayala, C. P. 11340. Ciudad de México. Author Mateo-Cid, Luz Elena Instituto Politécnico Nacional, Escuela Nacional de Ciencias Biológicas, Departamento de Botánica. Campus Santo Tomas. Carpio y Plan de Ayala, C. P. 11340. Ciudad de México. text Phytotaxa 2018 2018-03-27 345 3 179 218 http://dx.doi.org/10.11646/phytotaxa.345.3.1 journal article 10.11646/phytotaxa.345.3.1 1179-3163 13708555 Udotea cyathiformis var. flabellifolia D.S. Littler & M.M. Littler 1990: 220 Type locality:— PANAMA . San Blas Island. Morphology :—Thalli to 8 cm tall, anchored on substrata by a bulbous rhizoidal mass. Stipe cylindrical 10–15 mm length, 2–5 mm diameter, and flattening towards the blade. Evident transition between the stipe and blade. Blade fan-shaped or orbicular, grass green, slightly wider ( 1.5–8 cm ) than longer ( 1–6 cm ), lower margin ovate o truncate, multistratose, ecorticate, lightly calcified, and clearly zonate (Figs. 31, 32). Anatomy: — Blade siphons without lateral appendages, dichotomously branched, 45–55 μm in diameter, one of the siphons of the dichotomy gives rise to another dichotomy and the other continues to grow thus forming sub-dichotomies (Fig. 33). Distance between each dichotomy varies from 1300 to 2500 μm, supra dichotomous constrictions 19–27 μm length, 15–25 μm in diameter. Stipe siphons adjacent to lateral appendages 50–74 μm in diameter, appendages peduncle 70–250 μm length, 25–40 μm in diameter. Appendices arranged irregularly and dichotomously branched 2–3 times, with distorted digitate apices ( Fig. 34 ). FIGURES 34 . U. cyathiformis var. flabellifolia . 34) stipe lateral appendages. FIGURES 35–40 . U. dixonii . 35–37) external morphology, 38) blade siphon showing the opposite lateral appendages, 39) blade lateral appendages, 40) stipe lateral appendages. FIGURES 41–42 . U. dotyi . 41) external morphology, 42) blade siphons showing the lateral appendages arrangement. Reproduction: — Vegetative. Material examined :— MEXICO . Quintana Roo , Santa Rosa, 9 September 2016 , J . A . Acosta Calderón, L . E . Mateo Cid, A . C . Mendoza González, ENCB 23110. MEXICO . Quintana Roo , Santa Rosa, 12April 2015 , J . A .Acosta Calderón, L . E . Mateo Cid, A . C . Mendoza González, ENCB 23111. MEXICO . Quintana Roo , Punta Akumal, 16 December 2014 , J . A . Acosta Calderón, L . E . Mateo Cid, A . C . Mendoza González, ENCB 23112. MEXICO . Quintana Roo , Cayo Valencia, 16 August 2012 , J . A . Acosta Calderón, L . E . Mateo Cid, A . C . Mendoza González, ENCB 20887. MEXICO . Campeche , Playa Villamar, 25 January 2016 , J . A . Acosta Calderón, L . E . Mateo Cid, A . C . Mendoza González, ENCB 23109. MEXICO . Campeche , Payucán, 25 January 2016 , J . A . Acosta Calderón, L . E . Mateo Cid, A . C . Mendoza González, ENCB 23108. MEXICO . Campeche , Punta Xen, 20 June 2014 , J . A . Acosta Calderón, L . E . Mateo Cid, A . C . Mendoza González, ENCB 23107. Geographic distribution: — Panama , Cuba , Brazil , Mexico . Habitat : — Rocky in reef lagoons and sandy bottoms associated with sea grass meadows. Subtidal to 2 m depth. Comments: — Udotea cyathiformis var. flabellifolia is distinguished by flabellate blade and the deformed stipe appendages in comparison with the cup shape of the parental specie ( U. cyathiformis ) and spatulate shape of the sublittoralis form. The shape of the stipe appendages agrees which those described by Littler & Littler (1990) . Santos & Nunes (2014) provided detailed information about the morphology of this taxon and its occurrence in Brazil . This taxon has been recorded only in the Quintana Roo coast ( Acosta-Calderón et al . 2016 ), thus, in this paper the distribution of U. cyathiformis var. flabellifolia is extended to the Quintana Roo coast and is recorded for the first time for the Campeche littoral.